Although psoriatic arthritis is today recognized and as a distinct disease and pathological state based on its natural evolution, prognosis, and response to available modes of treatment, its consideration and present status as a distinct and separate clinical entity separate from either psoriasis and/or rheumatoid arthritis required both time and in-depth medical knowledge. In retrospect, the first detailed description of psoriatic arthritis appeared in the doctoral thesis of Charles Bourdillion [Psoriasis et Arthropathies, These de Paris, Volume 298, 1988]; and in several mid-19th century case reports of a unique relationship between psoriasis and arthritis published by 1904 [Menzen, J., Arch. Dermatol. Syph. 70:239-240 (1904)]. For about 30 years thereafter, the idea of psoriatic arthritis being an individual and discrete entity, as opposed to the coincidental occurrence of rheumatoid arthritis and psoriasis, was not generally accepted. Consequently, it was not until the demonstration of rheumatoid factor (RF) in the serum of most patients with typical rheumatoid arthritis in 1948 that the distinction became firmly established. The demonstration and meaning of rheumatoid factor (RF) divided inflammatory arthritis into seropositive and seronegative groupings. Consequently, the realization that the majority of patients with coincident psoriasis and arthritis were in fact seronegative, coupled with the introduction of specific and reliable criteria for the diagnosis of rheumatoid arthritis itself, then firmly established psoriatic arthritis as a separate and distinct disease entity [Rose et al., Proc. Soc. Exp. Biol. Med. 68:1-6 (1948); Ragan, C., Arthritis And Allied Conditions, (J.L. Hollander and D.J. McCarthy, editors) 8th Edition, Lee & Febiger, Philadelphia, 1972; Ropes et al., Bull. Rheum. Dis. 7:121-124 (1956); and Ropes et al., Bull. Rheum. Dis. 9:175-176 (1959)].
Today, rheumatologists have generally accepted the concept of distinctive clinical and radiological features for psoriatic arthritis; and employ them to identify subjects suffering from psoriasis alone and to distinguish those persons suffering from either seronegative or seropositive rheumatoid arthritis without psoriasis. A series of clinical characteristics suggestive of psoriatic arthritis have been developed and verified. Similarly, a detailed description and evaluation of the pathology, etiology, clinical features, patterns of disease onset and distribution, laboratory tests, and radiographic findings of psoriatic arthritic have been extensively investigated and documented. A comprehensive and well documented description of these diagnostic, clinical, and pathological developments and findings identifying psoriatic arthritis as a distinctive disease state and entity is provided by Robert N. Bennett in Arthritis And Allied Conditions, A Textbook Of Rheumatology, (Daniel J. McCarthy, Editor) Lee & Febiger, 11th Edition, 1989, pages 954-971, the text of which is expressly incorporated by reference herein.
Psoriatic arthritis can afflict humans with varying degrees of suffering and debilitation. Most patients with psoriatic arthritis have mild disease states affecting only a few joints and follow a rather episodic course. The range of symptoms and duration of disease may extend to forms considered mild, or acute, or even severe in the extreme cases. Many cases of mild disease are well controlled using aspirin or non-salicylic acid substitutes available without prescription as anti-inflammatory agents. In patients with only a few involved joints, corticosteroids injected locally, both into joints and into tendon sheaths have been effective. In the small number of patients (about 5%) developing severe, destructive inflammation that leads to marked disability, a number of different therapeutic approaches have been attempted. Photochemotherapy using oral 8-methoxypsoralenes, followed 2 hours later by photosensitization using ultraviolet light type A (PUVA) has been occasionally successful [Perlman et al., Ann. Intern. Med. 91:717-722 (1979)]. Similarly, high dose methotrexate administered parenterally [Black et al., JAMA 189:743-747 (1964)]has proven useful. More recent approaches and therapeutic compositions have included: chiral ester compounds of naproxen and naproxol [British Publication No. 2,204,868 printed Nov. 23, 1988]; the inhibiting of interleukin-1 production by monocytes [U.S. Pat. No. 4,778,806]; new substituted phenol compositions useful as anti-inflammatory and anti-arthritic compositions [U.S. Pat. No. 4,708,966]; a polyvalent non-specific immunostimulating vaccine comprising purified protein derivatives from rabies and snake venom [U.S. Pat. No. 4,657,761]; the treating of adrenal glands and affected joints daily with decimetre band electromagnetic fields [Soviet Union Patent No. 1,210,847 printed Feb. 15, 1986]; 6-alkoxy-2-naphthohydroxamic acid compounds useful as lipoxygenase inhibitors [U.S. Pat. No. 4,605,669]; 3-dimetblycarbamoylthyazolo-(4,5-a)-pyridine derivatives [British Patent No. 2,151,623]; pyrazolo-pyridine 3-carboxylic acid derivatives [British Patent No. 2,153,818]; immunosuppressive agents including tetrahydro-1,3-thiazine-4-one compounds [U.S. Pat. No. 4,352,929]; 2(4-(4-chlorophenyl)-benzelyoxy)-2-phenyl-acetic acid derivatives [U.S. Pat. Nos. 4,304,788 and 4,310,544]; and omega-hydroxy-carbonyl-alkyl substituted-dithio-carbanilates active as immunosuppressive agents [U.S. Pat. No. 4,166,866].
The mode and manner of developments and therapeutic treatments for effectively treating psoriatic arthritis thus is markedly different from the comparably intense investigations for effectively treating hyperproliferative skin disorders such as psoriasis itself. Exemplifying the degree of difference and approach has been the therapeutic development of using biologically active vitamin D analogues and metabolites as therapeutic agents.
The initial breakthrough in this field was the demonstration that topical application of radiolabelled 1,25-dihydroxy-7-dehydrocholesterol followed by phototherapy resulted in the detection of tritiated 1,25-dihydroxy vitamin D.sub.3 in the circulation. The topical application of such vitamin D analogues has been suggested as an effective method of therapy for diseases involving calcium, phosphorous, and bone metabolism problems [Holick et al., New England Journal Of Medicine 303:349-354 (1980); U.S. Pat. No. 4,230,701 and 4,335,210]. Subsequently, a specific biological function for 1 ,25-dihydroxy-vitamin D.sub.3 intracutaneously was demonstrated [Clemens et al., J. Clin. Endocrinol. Metab. 56:824-830 (1983); Morimoto et al., Arch. Dermatol. 125:231-234 (1989)]. In addition, it has been shown that the topical application of 1 -hydroxycholecalciferol, 1,25-hydroxychole-calciferol, 24,25-dihydroxycholecalciferol, and other derivative forms individually are directly effective agents in the skin of persons afflicted with contact dermatitis [European Patent Publication No. 0129003; see also Vitamin D Molecular, Cellular, And Clinical Endocrinology, Walter deGruyter & Company, Berlin, Germany, 1988, pp 300-319].
The most recent developments and therapeutic uses for vitamin D analogues and metabolites have been extended to include a variety of other clinical conditions including osteoporosis, rickets, rheumatism, and anti-proliferative agents effective against tumors. Representative of the variety and degree of these vitamin D developments are the following printed publications: European Patent Publication Nos. 250,755 (880107); 1184112 (860611); 205028 (861217); 85112679 (851007); and 87115258 (871019); Japanese publication No. 62004262 (870110); U.S. Pat. Nos. 4,341,774; 4,610,978; 4,613,594; 4,728,643.
It is abundantly clear, therefore, to clinical practitioners and research investigators in the art, that because of the major clinical and pathological distinctions and characteristics which identify and separate psoriatic arthritis from the related pathologies of psoriasis and rheumatoid arthritis individually, there has accordingly been no reason or expectation that the developments and uses of vitamin D analogues and metabolites might have any value or effectiveness on the clinical condition recognized distinctively as psoriatic arthritis. For this reason, and, because effective therapeutic treatments and compositions for psoriatic arthritis continue to be needed especially for those patients suffering from severe, debilitating forms, the possibility of applying vitamin D therapeutic treatments and compositions as therapies for psoriatic arthritis, stands as both unforeseen and unexpected developments and achievements of merit.